Insect Life

256 INSECT LIFE

XVIII

fresh materials from outside, tearing away a corner
of the protecting curtain, and through this window
grasping the materials needed. The cocoon is still
incomplete—wide open at the upper end and without
the spherical cap needed to close it. For this final
bit of work the grub provides itself abundantly with
sand, and then pushes away the heap before the
entrance. A silken cap is now woven and fitted
close to the mouth of this primitive basket, On this
silken foundation are deposited, one by one, the sand
grains kept in the interior and cemented with silk-
spittle. This lid completed, the larva has only to
give the last finish to the interior of the dwelling
and glaze the walls with varnish, to protect its tender
skin from the roughness of the sand.
The hammock of pure silk and the cap which
later closes it are evidently only scaffolding intended
to support the masonry of sand and to give it a
regular curve. One might compare them to the
constructions used by builders when making an arch
or vault. The work being completed, the silken
support disappears, partly lost in the masonry, and
partly destroyed by contact with rough earth, and
no trace remains of the ingenious method employed
to put together a construction perfectly regular, yet
made of a material so little coherent as is sand.
The spherical cap which closes the original basket is
a separate work, adjusted to the main body of the
cocoon. However well the two pieces are fitted and
soldered, the solidity is not such as the larva would
obtain had it built the whole dwelling continuously.
Thus, on the circumference of the cover there is a
circular line less capable of resistance, but this is not